The present invention relates generally to measuring the response of a system to an applied excitation signal and more specifically to measuring the rate of decay of oscillation in mechanical structures, acoustical enclosures, and electrical circuits. Since the rate of decay generally follows an exponential curve, a composite linear slope display on an oscilloscope may be obtained for a wide dynamic range by log conversion of the exponential decay data.
In the past, decay rate meters have been designed to terminate the excitation energy and to initiate alternate production of the logarithms of the decaying data signal and then of an adjustable reference decay rate signal. The operator then adjusted the reference decay rate signal in an iterative process until its slope on the oscilloscope appeared to coincide with that of the alternatively displayed decaying data signal. The operator then read the decay rate of the adjusted reference decay rate signal from an indicator dial.
Further, previous decay rate meters have been subject to nonlinear inaccuracies in the reference decay rate signals. The signals were generated by logarithmic means from a reference signal subject to intrinsic minor fluctuations which caused the generated reference decay rate signals to vary from the ideal signal.